The present invention relates to a piezoelectric/electrostrictive device having a movable portion being operated based on a displacement of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device capable of detecting a displacement of the movable portion by the piezoelectric/electrostrictive element, and more particularly relates to a piezoelectric/electrostrictive device which is superior in mechanical strength, impact resistance, and humidity resistance and in which the movable portion can be efficiently operated in a large magnitude.
In recent years, in the fields of optics, magnetic recording, precision machining, and the like, a displacement element capable of adjusting an optical path length or a position in sub-micron order has been required, and development has progressed of a displacement element utilizing a displacement due to the inverse piezoelectric effect or electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material, for example, a ferroelectric substance or the like.
For example, as shown in FIG. 2, a piezoelectric actuator 21 in which a fixing portion 25, a movable portion 24 and a bridge beam 26 connecting the two, are integrally formed by providing a hole 28 on a board-like body composed of a piezoelectric/electrostrictive material, and an electrode layer 22 is further provided on the bridge beam 26, is disclosed in JP-A-10-136665.
In the actuator 21, when a voltage is applied to an electrode layer 22, the movable portion 24 can have an arc-shaped displacement or a rotational displacement in the plane of the board-like body, since the bridge beam 26 expands or contracts in a direction connecting the fixing portion 25 with the movable portion 24 by the inverse piezoelectric effect and the electrostrictive effect.
However, in the actuator 21, there is a problem that an operational quantity of the movable portion 24 is small, since the displacement in the expanding or contracting direction, namely, the in-plane direction of the board-like body of the piezoelectric/electrostrictive material, is transmitted per se to the movable portion.
Further, the actuator 21 has another problem that the actuator 21, having all the members thereof constituted with a piezoelectric/electrostrictive material which is fragile and comparatively heavy, is low in mechanical strength, and inferior in handling property, impact resistance and humidity resistance, and in addition the actuator 21 per se is heavy and is easily subjected to an effect of harmful vibrations, for example, residual vibrations or vibrational noises under high speed operation.
In order to solve above-described problems of the actuator 21, a proposition is made that the hole 28 is filled with an elastic filler; it is apparent, however, that efficiency of the displacement due to the inverse piezoelectric effect or the electrostrictive effect is lowered when the filler is added.
The present invention is made in view of such problems of the conventional art, and an object of the present invention is to provide: a displacement element in which a movable portion can be operated in a large magnitude, and which is hardly subject to an effect of harmful vibrations in operation, and is superior in mechanical strength, handling property, impact resistance, and humidity resistance; a sensor element capable of detecting vibrations of the movable portion in fine accuracy; and a fabricating method for the elements.
According to the present invention, firstly provided is a piezoelectric/electrostrictive device comprising a driving portion to be driven by a displacement of a piezoelectric/electrostrictive element, a movable portion to be operated based on driving of the driving portion, and a fixing portion for holding the driving portion and the movable portion, said piezoelectric/electrostrictive device being characterized in that the driving portion is formed of a pair of thin plates facing each other and a film-like piezoelectric/electrostrictive element formed on an outer surface of at least one thin plate of the thin plates, the fixing portion is coupled with the movable portion via the driving portion, a hole is defined by an inner wall of the driving portion, an inner wall of the movable portion, and an inner wall of the fixing portion, and a ratio a/b of the thickness a of the piezoelectric/electrostrictive device and the width b of the piezoelectric/electrostrictive device is 0.5 to 20.
Further, in the present invention provided is a piezoelectric/electrostrictive device characterized in that a ratio e/a of the maximum length e of a length of a hole in parallel with the longitudinal direction of the piezoelectric/electrostrictive device and the thickness a of the piezoelectric/electrostrictive device is 0.5 to 10, more preferably a ratio a/b of the thickness a of the piezoelectric/electrostrictive device and the width b of the piezoelectric/electrostrictive device is 1 to 10, and a ratio e/a of the maximum length e of the length of the hole in parallel with the longitudinal direction of the piezoelectric/elec-trostrictive device and the thickness a of the piezoelectric/electrostrictive device is 0.7 to 5.
Although a shape of the movable portion or the fixing portion changes depending on the mode of application as an element, normally, it is preferable to be in rectangular solid form. Further, one having at least two driving portions is preferable, since function as a plurality of elements can be effectively performed. A piezoelectric/electrostrictive element to be mounted on the driving portion is preferably a laminated-type piezoelectric/electrostrictive element laminated by a lower electrode, a piezoelectric/electrostrictive film, and an upper electrode. Further, more preferable is a piezoelectric/electrostrictive element in which the piezoelectric/electrostrictive element comprises a piezoelectric/electrostrictive film, and a first electrode and a second electrode each of a comb-type structure, and the first electrode and the second electrode are structured to alternatively bite with a gap of a predetermined width between each tooth of respective combs. A piezoelectric/electrostrictive device constituted of ceramics with a movable portion, thin plates, and a fixing portion integrally formed is preferable from the standpoint of fabricating cost. Further, it is preferable that the piezoelectric/electrostrictive device be made of a laminated body.
According to the present invention, secondly provided is a piezoelectric/electrostrictive device comprising a driving portion to be driven by a displacement of a piezoelectric/electrostrictive element, a movable portion to be operated based on driving of the driving portion, and a fixing portion for holding the driving portion and the movable portion, wherein the piezoelectric/electrostrictive device is characterized in that the driving portion is formed of a pair of thin plates facing each other and a film-like piezoelectric/electrostrictive element formed on an outer surface of at least one thin plate of the thin plates, the fixing portion is coupled with the movable portion via the driving portion, a hole is defined by an inner wall of the driving portion, an inner wall of the movable portion, and an inner wall of the fixing portion, and the thickness a of the piezoelectric/electrostrictive device is 100 xcexcm to 2000 xcexcm, and the width b of the piezoelectric/electrostrictive device is 100 xcexcm to 2000 xcexcm.
Further, provided are a piezoelectric/electrostrictive device characterized in that the thickness a of the piezoelectric/electrostrictive device is 200 xcexcm to 1000 xcexcm and the width b of the piezoelectric/electrostrictive device is 100 xcexcm to 500 xcexcm, and a piezoelectric/electrostrictive device characterized in that the thickness d of the thin plate of the piezoelectric/electrostrictive device is 2 xcexcm to 100 xcexcm, and further a piezoelectric/electrostrictive device characterized in that the maximum length e of a length of a hole in parallel with the longitudinal direction of the piezoelectric/electrostrictive device is 300 xcexcm to 3000 xcexcm, and furthermore a piezoelectric/electrostrictive device characterized in that the length f of the movable portion in parallel with the longitudinal direction of the piezoelectric/electrostrictive device is 50 xcexcm to 2000 xcexcm.
According to the present invention, thirdly provided is a piezoelectric/electrostrictive device comprising a driving portion to be driven by a displacement of a piezoelectric/electrostrictive element, a movable portion to be operated based on driving of the driving portion, and a fixing portion for holding the driving portion and the movable portion, said piezoelectric/electrostrictive device being characterized in that the driving portion is formed of a pair of thin plates facing each other and a film-like piezoelectric/electrostrictive element formed on at least a part of an outer surface of at least one thin plate of the thin plates, and having the width same as the width of the thin plate and/or a length which exceeds the length of the thin plate portion constituting the driving portion and reaches at least to a part of the moving portion, the fixing portion is coupled with the movable portion via the driving portion, and a hole is defined by an inner wall of the driving portion, an inner wall of the movable portion, and an inner wall of the fixing portion.
A piezoelectric/electrostrictive device in which a film-like piezoelectric/electrostrictive element formed on at least a part of an outer surface of at least one thin plate of the thin plates has the width same as the width of the thin plate is preferred because a generating force of the driving portion can be increased and there is an advantage that a displacement in larger magnitude can be obtained. Also preferable is a piezoelectric/electrostrictive device in which a ratio a/b of the thickness a of the piezoelectric/electrostrictive device and the width b of the piezoelectric/electrostrictive device is 1 to 10, and a ratio e/a of the maximum length e of a length of the hole in parallel with the longitudinal direction of the piezoelectric/electrostrictive device and the thickness a of the piezoelectric/electrostrictive device is 0.7 to 5. In this embodiment, in the same reasons as described above, preferable is a piezoelectric/electrostrictive device of which a movable portion and a fixing portion are in rectangular solid shape, and preferable is a piezoelectric/electrostrictive device having at least two driving portions. Furthermore, preferable is a piezoelectric/electrostrictive device having a length of a film-like piezoelectric/electrostrictive element formed on at least a part of an outer surface of at least one thin plate of the thin plates, which exceeds the length of the thin plate portion constituting the driving portion and reaches to at least a part of the movable portion. In this case as well, preferable is a piezoelectric/electrostrictive device in which a ratio a/b of the thickness a of the piezoelectric/electrostrictive device and the width b of the piezoelectric/electrostrictive device is 1 to 10, and a ratio e/a of the maximum length e of a length of the hole in parallel with the longitudinal direction of the piezoelectric/elecrostrictive device and the thickness a of the piezoelectric/electrostrictive device is 0.7 to 5. Of course, in the same reason as described above, preferable is a piezoelectric/electrostrictive device of which a movable portion and a fixing portion are in rectangular solid form, and preferable is a piezoelectric/electrostrictive device having at least two driving portions.
Furthermore, according to the present invention, fourthly provided is a fabricating method of a piezoelectric/electrostrictive device comprising a driving portion composed of thin plates facing each other and a film-like piezoelectric/electrostrictive element formed on the surface of at least one thin plate of the thin plates, and a fixing portion and a movable portion in rectangular solid form, and the thin plates facing each other are spanned so that side surfaces of the movable portion and the fixing portion are continuous, said fabricating method of the piezoelectric/electrostrictive device being characterized by including steps of preparing a green-sheet laminated body comprising at least one green sheet constituting thin plate and at least one green sheet with at least one hole formed thereon, sintering the green-sheet laminated body, and forming a piezoelectric/electrostrictive element on an outer surface of thin plates of the sintered body obtained.
Further, provided are a fabricating method of a piezoelectric/electrostrictive device wherein at least one green sheet constituting thin plates is a green sheet constituting the thin plates laminated by at least one green sheet with the at least one hole formed thereon, a fabricating method of a piezoelectric/electrostrictive device wherein at least one green sheet constituting thin plates is composed only of a green sheet constituting the thin plates, and at least one green sheet with at least one hole formed thereon is laminated by a desired number of green sheets each with at least one hole formed thereon, and a fabricating method of a piezoelectric/electrostrictive device wherein at least one green sheet with the at least one hole formed thereon is laminated with at least one green sheet constituting thin plates, and a fabricating method of a piezoelectric/electrostrictive device wherein a green-sheet laminated body is a green sheet including at least one green sheet with at least one hole formed thereon, and at least one green sheet with at least one hole formed thereon is a green sheet including one green sheet constituting thin plates, and further a piezoelectric/electrostrictive device is obtained by laminating the green sheet with at least one hole formed thereon through intermediary of one or a plurality of the laminated body.
In the meantime, provided are a fabricating method of a piezoelectric/electrostrictive device wherein a sintered body with a piezoelectric/electrostrictive element formed on an outer surface of thin plates is further cut into each desired units and the cut body is heat-treated at 300xc2x0 C. to 800xc2x0 C., and a fabricating method for a piezoelectric/electrostrictive device wherein, when laminating a green sheet with at least one hole formed thereon in at least a plurality of layers, a green sheet, mounted on a plastic film, with at least one hole formed thereon, is laminated on the outer-most layer of the laminated body of green sheets each with at least one hole formed thereon, and the hole is accurately aligned, and the fabricating method includes a step of removing the plastic film. The plastic film is preferably a poly(ethylene terephthalate) film.
In a piezoelectric/electrostrictive device according to the present invention, it is preferable, as aforementioned, to have a movable portion, thin plates, and a fixing portion in integrally formed ceramics, and it is more preferable to have the moving portion, the thin plates, and the fixing portion composed of fully-stabilized zirconia or partially-stabilized zirconia, and it is specifically preferable to have a laminated body at least comprising a movable portion, thin plates, and a fixing portion.
Further, in a piezoelectric/electrostrictive device according to the present invention, it is preferable that a piezoelectric/electrostrictive film constituting a piezoelectric/electrostrictive element is composed of materials including lead zirconate, lead titanate, and lead magnesium niobate as a major component, and materials composed of sodium bismuth titanate as a major component is also preferable. Details of materials to be used is hereinafter described.
Furthermore, according to the present invention, provided is an optical shutter characterized in that the optical shutter is for controlling transmission and shielding of the light by relatively moving two shields, and at least one of the shields is mounted on a movable portion of the above-described piezoelectric/electrostrictive device.